1. Field of the Invention
The present invention relates to an apparatus and method for manufacturing integrated circuits. More specifically, the present invention relates to an apparatus and method to enhance wafer throughput in semiconductor device processing.
2. Description of Related Art
Pre-processing is commonly performed on semiconductor wafers to remove surface and absorbed impurities such as water vapor and other gases from the silicon wafers. If left to reside on and within the wafer, these impurities may result in defects in the integrated circuit. It has been established that gases and water vapor may be removed from the wafers by heating or baking the wafer at some elevated, predetermined temperature in a vacuum for a specified period of time.
Current wafer processing tools have focused on batch processing of multiple wafers, utilizing a single robotic arm for insertion and removal of the wafers from their holder or cassette. The wafers undergo radiated heat treatment in batch quantities, typically by exposure to heat from quartz lamps radiated through a transparent partition in a vacuumed chamber. The wafers are heated in bulk as a single process step. Prior designs teach of using the wafer carrier together with a load lock and vacuum wafer transport mechanism at more than one process module to provide a complete low-particulate wafer transfer system. However, the inherent design of these systems requires the wafers to be processed and heated in batch.
For example, in U.S. Pat. No. 5,388,944 issued to Takanabe, et al., on Feb. 14, 1995, entitled xe2x80x9cVERTICAL HEAT-TREATING APPARATUS AND HEAT-TREATING PROCESS BY USING THE VERTICAL HEAT-TREATING APPARATUS,xe2x80x9d a wafer loading and unloading chamber is taught for introducing wafers to a heat treatment section of a process tool. A plurality of wafers are loaded in a target object assembly or wafer cassette and inserted into a vertical-type reaction tube within which batch wafer heat-treatment is performed. A conveying apparatus, specifically a single robotic arm provided in a first load lock chamber, transports the wafers into and out of the reaction tube. A second load lock chamber secures and removes the wafers.
Similarly, in U.S. Pat. No. 5,380,682 issued to Edwards, et al., on Jan. 10, 1995, entitled, xe2x80x9cWAFER PROCESSING CLUSTER TOOL BATCH PREHEATING AND DEGASSING METHOD,xe2x80x9d a wafer processing cluster tool having one or more load-locks is taught with batch pre-heating modules that receive wafers from a cluster tool transport module. A pair of modules are operated such that one module can be initially loaded with wafers from the transport module and then heated as a batch. While this heating is taking place, the second preheat module or degas chamber can be loaded in a similar fashion with a second batch of wafers. After the first batch of wafers has been heated, the wafers from it are transferred to other processing stations and then transferred to a load-lock for removal.
The prior art designs have increased throughput to the semiconductor process by adding an additional wafer degas chamber to the cluster tool. However, these designs promote batch processing, which requires a station to be completely unloaded before reloading. Moreover, by using a batch process, each wafer in a loaded cassette must be degassed concurrently, and in a single process step. Furthermore, by utilizing radiated heat in a batch process, typically by employing quartz lamps, the prior art designs are not well-suited for uniform wafer heating, as the stacked wafers will tend to shield radiated energy from adjacent wafers.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an apparatus and process for degas of semiconductor wafers that does not rely on batch processing of the wafers.
It is another object of the present invention to provide an apparatus and process for degas of semiconductor wafers that promotes a sequential process, dividing the total degassing time over a number of cycles for each wafer.
A further object of the invention is to provide an apparatus and process for degas of semiconductor wafers utilizing a pass-through configuration that allows for the simultaneous exchange of wafers.
Another object of the invention is to provide an apparatus and process for degas of semiconductor wafers that uniformly heats wafers vertically aligned in their holders.
Still other advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects, which will be apparent to those skilled in art, are achieved in the present invention which is directed to in a first aspect, a method of degassing semiconductor wafers in a multi-station degas apparatus, comprising: lowering a heater and wafer holder assembly stack having slots for individual semiconductor wafers into a transfer/load chamber; loading a wafer into the heater and wafer holder assembly slot; removing at least one wafer from the heater and wafer holder assembly slot, such that the removed wafer may be individually processed while other wafers remain in the heater and wafer holder assembly; and, positioning the heater and wafer holder assembly into a degas chamber for degas treatment while the at least one removed wafer is exposed to other process steps in other stations of the multi station degas apparatus.
This method further comprises monitoring the temperature inside the slots through thermocouple channels from the heater and wafer holder assembly stack, monitoring and displaying the temperature using a user interface electrical connection. Removing a wafer comprises removing a single wafer at a time using a transfer robotic arm and a load robotic arm.
In a second aspect, the present invention is directed to a method of degassing semiconductor wafers in a multi-station degas apparatus, comprising: positioning a heater and wafer holder assembly stage having a plurality of wafer slots in a sequential manner through each of the wafer slots to the next available wafer slot; removing a first of a plurality of wafers from one of the wafer slots using a transfer robotic arm after the wafer has been subjected to a degas treatment in a degas chamber; re-positioning the heater and wafer holder assembly stage to receive a second wafer from the loader robotic arm; loading the second wafer in an available wafer slot using the loader robotic arm after the first wafer has been removed; retracting the robotic arms; sealing the heater and wafer holder assembly stage into the degas chamber; and degassing the second wafer in the heater and wafer holder assembly while the first wafer is subjected to other process stations within the multi-station degas apparatus.
The degassing of the wafers further comprises: closing a vacuum pump isolation valve; introducing process gases; initiating a timer; controlling pressure in the degas chamber; and, opening a by-pass valve after the degas chamber reaches a predetermined internal pressure.
In a third aspect, the present invention is directed to a multi-station degas apparatus for semiconductor wafer processing, comprising: a process degas chamber; a load/transfer chamber; a heater and wafer holder assembly stack having a plurality of slots, the heater and wafer holder assembly stack positionable within the degas chamber and the load/transfer chamber; a conduction heater in each of the plurality of slots for individual conduction heating of the wafers, a vertical motion bar and platform capable of moving the heater and wafer holder assembly stack to and from the chambers; at least two robotic arms for placing and removing wafers from the heater and wafer holder assembly stack; gas inlets for introducing process gases to the degas chamber; an o-ring positioned to seal the heater and wafer holder assembly stack and the platform when the heater and wafer holder assembly stack is raised into the degas chamber; a turbo-pump to extract water vapor and other contaminants from the degas chamber; and, pressure, temperature and positioning control devices.